This question has a lot in common with the problem solving questions.

The answer must be clear, absolutely unmistakable as a statement of value.

Nobody should need to ask for any further information, except relatively minor details, having got the point. (Professionals are nosy, and you may well be getting good positive feedback, because they're genuinely interested.)

You need to:

Don't:

• Falsify or mislead, ever, under any circumstances
• Be coy about telling people what a good job you did
• Go off topic,
• Be vague about anything important
• Leave any part of the storyline out

We need to go through this in a bit of detail, because it's fairly easy to trip over yourself in the rush to tell your story.

Believe it or not, your main asset at this point is the interview panel.

You're speaking to at least one, probably two, professionals in your field. They know how to put anything you tell them about achievements into context with the position. They also know where you are on your career path, because they've been there and they really have done that.

This is also the point where you can get technical, talk shop, and show that you know your stuff very effectively. The achievements are business, and you can speak the language of business. This is actually a much more efficient form of communication, and saves enormous amounts of time. You can say a lot.

In interviews, there's a lot of pro forma language, filling in points, and specifically addressing things according to the interview requirements. It is a formal process, and the interview panel have to check off each point you cover, relative to their criteria.

(In some cases it is an actual check list, showing candidates satisfy specific requirements.)

At the achievement stage, that changes. You can now talk normally about your work, use common terms, and get down to business.

Define the achievement

This is a simple, direct, statement of what you did. You start by explaining what you did.

I increased sales by 120%.

You're actually introducing the achievement, defining the subject. There's no way of misunderstanding a statement like this. You make your point clearly.

Be specific about what happened, who, what, where and when

The obvious requirement is to explain what was done. Again, clarity is required.

I was doing floor selling at ABC Motors last year, when we got a new shipment of Mercedes sports models. I sold the whole shipment, personally, None of the other salespeople sold one.

Not vague, is it? This is an obvious personal achievement. Any car dealer would want to know how you did that, particularly with a big name brand. You're on good safe ground here, because you have the sales figures to prove it.

Put it in context with your position

The degree of difficulty in any job is relative to the position in the hierarchy. If you're performing way over your rank, you're doing very well.

I was the junior salesperson at ABC, and I'd only been there for a year when this happened.

Obviously, this interviewee has talent. There's more information required, but so far this is a standout performance, both on the job and in the interview.

Be clear about what you did, and how you did it

At this point the interview panel needs to know how you achieved your result.

We have some big corporate clients, including some top range companies. I was on the floor when they saw the new range, and did all the sales myself. I found out later that they'd told their friends about our new models, and mentioned me as the person to talk to about the new Mercedes. So I did the selling, and followed up any queries, and explained the new features…( a brief amount of detail is permissible here, just to show what you did)

Fair to say that maybe the interviewee got lucky, or maybe this is a very good salesperson. Either way, the achievement is not to be ignored. It's also obvious the sales were done professionally, with a lot of actual sales work involved.

Be absolutely clear about what a great achievement it was

Now is not the time to be shy about driving the nail in, and really spelling out what you achieved.

So we sold $2,000,000 of Mercedes in a week. Mercedes gave us an award, top sales of the month, and I got a promotion, specializing in Mercedes. They even gave us a special deal, and we're now getting better margins on our shipments.

The basic confirmation of career achievement is recognition, and here it is, by the ton. The interviewee has nailed the question, too.

The Don'ts are very important.

• Don't falsify or mislead, ever, under any circumstances. You are talking to professionals, and they can find information you may not even know exists, if they want. They may not even need to check, because most are up to date on information inside their field. Very few liars survive, and this particular question is the one that always finds them.
• Don't be coy about telling people what a good job you did. There's a real problem here, if you look like you're withholding information. The interviewers may think you're lying, or that you're taking credit for someone else's work. Modesty is a virtue, but in most jobs it's an unpaid virtue at best.
• Don't go off topic. You're reducing the amount of information you're providing about your achievement, which is the actual question. It also eats up time, messes up the continuity of your answer, and you may have to cram everything you wanted to say into a few inadequate gasps of rushed information at the end.
• Don't be vague about anything important. A statement like 'Sales figures went through the roof' from our car sales person may sound important, and is a statement of fact. But if that information was expressed like this, what does it mean? In this form, it's almost meaningless. There's nothing specific, no value. Compared to the other way of stating an achievement, it's useless, and the interviewers may be wondering why they have to dig information out of this person. Communications skills are basic, and this isn't communication.
• Don't leave any part of the storyline out. Also basic is the fact that interviewers need to be able to put together a clear picture of your achievement. If they don't know how something was done, they don't have an important part of the story. Leaving things out is a very effective way of not answering a question. It's also at risk of looking like a lie. You know what you did, but you don't know how you did it, or aren't prepared to say? It doesn't look good.